This invention relates to a seal. In particular the invention relates to a seal assembly. The invention further relates to a method of controlling a spacial relationship between two sealing surfaces. Still further, the invention relates to a machine incorporating a seal assembly.
According to a fast aspect of the invention there is provided a seal assembly which includes
a support member;
a first seal element defining a first sealing surface;
a second seal element which is rotatable relative to the support member and the first seal element, the second seal element defining a second sealing surface which together with the first sealing surface forms a seal; and
displacement means including at least one electromagnet acting between the first seal element and the support member to permit displacement of the first seal element relative to both the support member and the second seal element.
The seal assembly may include a sensor means for sensing a displacement of the second seal element from a first datum position.
The seal assembly may include control means operably connected to the sensor means and the displacement means, the control means being operable to control the displacement means to maintain the first sealing surface in a predetermined spacial relationship with the second sealing surface.
The seal assembly may include a biasing means for biasing the first seal element in a predetermined direction. The biasing means may bias the first seal element towards the second seal element. Instead, the biasing means may bias the first seal element away from the second seal element. The biasing means may be configured to exert a force which is a function of a displacement of the biasing means from a second datum position.
The displacement means may include a plurality of electromagnets in spaced relationship with respect to one another and the control means may be operable to control each of the electromagnets. Then, the sensor means may include a plurality of sensors, a sensor being associated with each of the electromagnets. The control means may be operable to control each of the electromagnets independently. Instead, the control means may be operable to control sub-sets of the electromagnets in unison.
The first seal element may comprise an annular ring defining an annular first sealing surface and the second seal element may define an annular second sealing surface. Then, the seal assembly may include a rigid carrier member on which the first annular seal element is mounted, the electromagnets being operatively coupled with the carrier member and angularly spaced with respect thereto to permit displacement of the carrier member relative to the support member.
Further, each of the electromagnets of the displacement means may have a core element displaceable with respect to a coil, one of the core element and the coil being connected to the carrier member of the first seal element and the other of the core element and the coil being connected to the support member.
In one embodiment of the invention the seal assembly may provide a seal on a rotating element of a machine. Then, the first seal element may comprise an annular ring defining an annular first sealing surface. The second element may be the rotating element of the machine and may define a second sealing surface which also comprises an annular ring. The first annular seal element may be mounted on a rigid carrier member. The displacement means may include a plurality of electromagnets coupled with the carrier member and angularly spaced on the carrier member. The electromagnets of the displacement means may have a movable core element. The movable core element may be attached to the carrier member of the first seal element. The coils of each electromagnet may be attached to a support member which may be fixed in position. It will be appreciated that by controlling the current in the coil of each electromagnet the magnetic flux of the electromagnet may be selectively varied thereby selectively varying the force on the core element of the electromagnet. Thus, a lateral force of a preselected strength may be applied to the first seal element at the position of each electromagnet. It will further be appreciated that by selectively varying the lateral force of each electromagnet the entire annular first seal element may be displaced so that a plane defined by the first seal element is displaced in a direction perpendicular to the plane. Instead, the plane may be tilted in a preselected direction with respect to a symmetrical axis of the first seal element.
In a particular embodiment of the invention, the second seal element may comprise a downstream portion of a power generator gas turbine. It will be appreciated that a turbine rotating on a shaft about a rotation axis may move on its bearings both axially and radially. In addition, the longitudinal axis of the turbine may precess. It will further be appreciated that the gap between a downs sealing surface defined on a downstream end of the turbine rotor (providing the second seat element) and a sealing surface of an annular seal element (providing the first seal element) sealing on the said downstream sealing surface will vary with the displacement of the turbine rotor. Accordingly, if the said gap is to be maintained within predetermined limits, the first seal element must be allowed to move in a manner related to the movement of the rotating second sealing surface of the turbine rotor. The sensing means may be operable to sense displacement of the turbine shaft or any rotating components rotatably fixed to the shaft, such as the downstream sealing surface of the turbine rotor. Instead, the sensing means may comprise a plurality of sensors which sense the distance between the first and second sealing surfaces at preselected locations.
According to a further aspect of the invention there is provided a combination comprising a gas turbine including a turbine rotor having a downstream end and a seal assembly as hereinbefore described, the second sealing surface of the seal assembly being arranged on the downstream end of the turbine rotor.
Then, the sensor means of the seal assembly may sense displacement of the second seal element from the first datum position directly. The sensor means of the seal assembly may include a plurality of sensors, each of which being operable to sense a distance between the first and second sealing surfaces at a respective preselected location, the position of the first sealing surface at the said location defining the first datum position.
Instead, the sensor means of the seal assembly may sense displacement of the second seal element from the first datum position indirectly by sensing a displacement from a datum position of a component of the gas turbine mechanically fast with the rotor thereof.
The combination may include biasing means for biasing the first seal element in a predetermined directions the at least one electromagnet being configured to displace the first seal element relative to the support member in a direction opposite to the predetermined direction.
Further, the biasing means may comprise an annular gas impermeable bellows arranged between the carrier member and the support member.
According to another aspect of the invention there is provided a method of controlling a spacial relationship between respective sealing surfaces of two seal elements, the method including the steps of sensing a displacement of one of the seal elements, which seal element is rotatable relative to a support member and to the other seal element, from a datum position; and displacing the other of the seal elements by means of a displacement means including at least one electromagnet acting between the other of the seal elements and the support member, the said other seal element being operatively coupled with the displacement means via the, or each, electromagnet to maintain a preselected spacial relationship between the two sealing surfaces.
The datum position may be defined by the sealing surface of said other seal element, and the method may include sensing the distance between the two sealing surfaces and displacing the said one seal element to maintain a preselected distance between the two sealing surfaces.
The displacement means may include a plurality of electromagnets and the method may include selectively varying the magnetic flux in each of the electromagnets.